Hitherto, various light-sensitive materials for electrophotographic photoreceptors have been proposed; and for laminate type electrophotographic photoreceptors where the light-sensitive layer is composed of separate charge generating layer and charge transporting layer, various organic compounds have been proposed as charge generating materials.
Recently, the demand for extending the light-sensitive wavelength range of organic photoconductive materials which have heretofore been proposed up to the near infrared wavelength range of semiconductor lasers (780 to 830 nm) so as to use the materials as a photoreceptor for a digital recording system such as a laser printer. From the viewpoint, squarylium compounds (as disclosed, e.g., in JP-A-49-105536 and JP-A-58-21414), triphenylamine trisazo compounds (as disclosed, e.g., in JP-A-61-151659) and phthalocyanine compounds (as disclosed, e.g., in JP-A-48-34189 and JP-A-57-148745) have been proposed as photoconductive materials for semiconductor lasers. (The term "JP-A" as used herein means an "unexamined published Japanese patent application").
Where organic photoconductive materials are used as light-sensitive materials for semiconductor lasers, they are needed to satisfy the conditions that the light-sensitive wavelength range is extended up to a long wavelength range and that the sensitivity and durability of the photoreceptors to be formed therefrom are good. The above-mentioned organic photoconductive materials do not sufficiently satisfy the conditions.
In order to overcome various drawbacks of the known photoconductive materials, the materials have been investigated with respect to the relationship between the crystal form and the electrophotographic characteristics. In particular, many reports relating to phthalocyanine compounds have heretofore been disclosed.
In general, it is known that phthalocyanine compounds have various crystal forms, depending upon the difference in the manufacture method and treating method, and that the difference in the crystal form has a great influence on the photo-electric conversion characteristics of phthalocyanine compounds. Regarding crystal forms of phthalocyanine compounds, for example, with respect to copper phthalocyanine, various crystal forms of .alpha., .pi., .chi., .rho., .gamma. and .delta. are known in addition to a stable crystal form of .beta.. It is also known that these crystal forms are mutually transferable to each other by mechanical strain force, sulfuric acid treatment, organic solvent treatment or heat treatment (for example, refer to U.S. Pat. Nos. 2,770,029, 3,160635, 3,708,292 and 3,357,989). JP-A-50-38543 describes the difference of crystal forms of copper phthalocyanine and electrophotographic characteristics of them. It mentions that e crystal forms of copper phthalocyanine have the highest sensitivity as compared with other .alpha., .beta. and .gamma. crystal forms of them
Regarding chlorogallium phthalocyanine, Denshishashin Gakkaishi (Journal of Electrophotographic Society), vol. 26 (3), 240 (1987) discloses crystal forms of chlorogallium phthalocyanine having particular Bragg angles. However, the disclosed ones are different from the novel crystals of the present invention with respect to the crystal forms of them and the publication is silent on the application of the disclosed crystals to electrophotography. JP-A-59-44053 and a bulletin of Shinkyo Gihoh CPM81-69, 39 (1981) describe application of chlorogallium phthalocyanine crystals to electrophotography; and JP-A 1-221459 describes chlorogallium phthalocyanine crystals having particular Bragg angles and an electrophotographic photoreceptor using them.
However, not only the above-mentioned chlorogallium phthalocyanines but also phthalocyanine compounds as heretofore been proposed are not sufficient in point of the light-sensitivity and durability when they are used as light-sensitive materials. In addition, with respect to manufacture of them, there are further problems that the operation for converting crystal forms of them is complicated and troublesome and control of crystal forms of them is difficult.
The present invention has been made in view of the above-mentioned problems in the prior arts.